This invention relates to medical equipment and in particular to a user interface for a defibrillator having separate manual and automated functions.
One frequent consequence of heart disease is the development of cardiac arrest associated with a heart arrhythmia, such as ventricular fibrillation. Ventricular fibrillation may be treated by delivering an electrical shock to the patient's heart through the use of a defibrillator. Cardiopulmonary resuscitation (CPR) is commonly used to maintain life support for victims of cardiac arrest until a defibrillator can be deployed to treat the arrhythmia.
The chances of surviving a cardiac arrest decrease rapidly over the time following the arrest. Quick response to a cardiac arrest by performing CPR and by administering a defibrillating shock is therefore of critical importance. The American Heart Association's "Chain of Survival" recites the following steps:
1. Early access to emergency care, such as by activating an emergency medical system (EMS); PA1 2. Early CPR initiated by a bystander or other first responder using basic life support (BLS) techniques to help the patient survive until more advanced care arrives; PA1 3. Early defibrillation; and PA1 4. Early advanced cardiac care. The benefits of this approach are discussed in more detail in Cummins, et al. "Improving Survival From Sudden Cardiac Arrest: the `Chain of Survival` Concept," 83 Circulation 1832-47 (May 1991).
EMS providers are playing an active role in implementing the Chain of Survival concept. Tiered EMS systems are emerging in many geographical areas, typically divided between first responders, BLS (basic life support) providers, and ACLS (advanced cardiac life support) providers, are emerging in many geographic areas. First responders and BLS providers, often called EMT(B) or EMT-basic, the front line personnel who are first to reach a patient, are now being trained and authorized to use automatic external defibrillators (AEDs) to provide early defibrillation.
AEDs deliver a high-amplitude current impulse to the heart in order to restore normal rhythm and contractile function in the patients who are experiencing ventricular fibrillation (VF) or ventricular tachycardia (VT) that is not accompanied by a palpable pulse. AEDs differ from manual defibrillators in that AEDs can automatically analyze the electrocardiogram (ECG) rhythm to determine if defibrillation is necessary. In nearly all AED designs, the first responder is prompted to press a shock button to deliver the defibrillation shock to the patient. Paramedic defibrillators often combine the AED and manual functions into one unit to allow for use by personnel with differing levels of training.
AEDs are designed to be used primarily by first responders who may not be trained in ACLS techniques. In the pre-hospital setting, these first responders may include emergency medical technicians trained in defibrillation (EMT-Ds), police officers, flight attendants, security personnel, occupational health nurses, and firefighters. AEDs can also be used in areas of the hospital where personnel trained in ACLS are not readily available. In such cases, it may be desirable to provide a paramedic defibrillator which operates in an AED mode with the manual functions disabled.
Having a simple, easily understood user interface in an AED is particularly important in applications where the first responder may have only infrequent need to use the AED. Because training and refresher courses may be relatively infrequent, coupled with a high stress emergency situation in which the AED is designed to be used in, the user interface design is therefore critical. A simple, interactive user interface for a AED is discussed in U.S. Pat. No. 4,610,254, "Interactive Portable Defibrillator", issued Sep. 9, 1986 to Morgan et al. and assigned to Physio-Control Corporation. The user interface taught by Morgan et al. prompts the operator with questions on an LCD display which are answered by pressing "YES" or "NO" buttons for interactive guidance through the patient analysis process. A separate button for "SHOCK" is pressed to deliver a defibrillation shock to the patient. The AED is automatically activated with the removal of the cover plate which exposes instructions placed on the underside of the cover plate.
In more recent AED designs such as the Heartstream Forerunner.RTM. defibrillator, the AED functions have been logically grouped into step 1, "power on"; step 2, "analyze"; and step 3, "shock." More sophisticated audio prompts have been added in addition to the visual prompts provided by the LCD display. The transition from step 1 to step 2 may be initiated by the defibrillator, such as upon detection of patient contact between the defibrillation electrodes to begin the ECG analysis as soon as possible. Proceeding from step 2 to step 3 according to the AED personality requires the user to press a shock button upon recognition of a shockable rhythm by the ECG analysis. In this way, the AED personality is commonly understood to mean semi-automatic rather than fully automatic defibrillation.
The step 1, 2, and 3 methodology, with some variation among manufacturers, is commonly understood and accepted as the AED personality. After step 3, the AED can continue the ECG analysis as a background process to watch for shockable rhythms and alert the user.
In many EMS systems, the next link in the Chain of Survival is provided with the arrival of ACLS trained paramedics on the scene equipped with full featured defibrillators/cardiac monitors ("paramedic defibrillators"). Alternatively, if no ACLS trained personnel are available, the patient is directly transported to a hospital emergency department where ACLS care can be provided. ACLS personnel typically use paramedic defibrillators which contain more advanced cardiac monitoring and analysis functions such as 3, 5, or 12 lead ECG monitoring, along with other functions such as cardiac pacing. These functions are manual functions requiring additional skill and judgment of the operator over that of the first responder.
The HP CodeMaster 100 defibrillator with shock advisory is an example of a manual defibrillator having AED functionality. While capable of performing dual roles both as an AED and a manual defibrillator, such a defibrillator may be not optimal for first responders. The manual and automatic modes are blended together on the same rotary switch on the front panel. The AED personality in such a defibrillator is designed more for a clinical environment for use by more skilled personnel and does not follow the more easily understood step 1-2-3 format outlined above.
It is desirable to have the ability to standardize on one type of defibrillator that may be used effectively by both first responder and ACLS personnel. Standardization helps to reduce the number and types of defibrillators in an EMS system in order to minimize support and administration costs. Because the training level and qualifications of BLS and ACLS personnel are different, the functions available on the defibrillator must necessarily be different. Therefore, it would be desirable to provide a defibrillator with an AED personality in terms of the step 1-2-3 format substantially maintained for the BLS personnel while logically segregating and restricting access to the manual functions to qualified ACLS personnel.